A general system error occurred: Not initialized

I try to add Traffic Rule for one of ports on DVS.

Body of my SOAP request looks like:

<?xml version="1.0" encoding="UTF-8"?>

<SOAP-ENV:Envelopexmlns:ns0="urn:vim25"

   xmlns:ns1="http://schemas.xmlsoap.org/soap/envelope/"

   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

   xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">

   <ns1:Body>

   <ns0:ReconfigureDVPort_Task>

   <ns0:_thistype="VmwareDistributedVirtualSwitch">dvs-52</ns0:_this>

   <ns0:port>

   <ns0:operation>edit</ns0:operation>

   <ns0:key>1196</ns0:key>

   <ns0:settingxsi:type="ns0:VMwareDVSPortSetting">

   <ns0:filterPolicy>

   <ns0:inherited>0</ns0:inherited>

   <ns0:filterConfig

   xsi:type="ns0:DvsTrafficFilterConfig">

   <ns0:inherited>0</ns0:inherited>

   <ns0:trafficRuleset>

   <ns0:enabled>1</ns0:enabled>

   <ns0:rules>

   <ns0:description>description

   </ns0:description>

   <ns0:sequence>1</ns0:sequence>

   <ns0:qualifier

   xsi:type="ns0:DvsIpNetworkRuleQualifier">

   <ns0:sourceAddress

   xsi:type="ns0:IpRange">

   <ns0:addressPrefix>

  255.255.255.255

   </ns0:addressPrefix>

   <ns0:prefixLength>0

   </ns0:prefixLength>

   </ns0:sourceAddress>

   <ns0:destinationAddress

   xsi:type="ns0:IpRange">

   <ns0:addressPrefix>

  255.255.255.255

   </ns0:addressPrefix>

   <ns0:prefixLength>0

   </ns0:prefixLength>

   </ns0:destinationAddress>

   <ns0:protocol>

   <ns0:negate>false</ns0:negate>

   <ns0:valuexsi:type="xsd:string">

  6

   </ns0:value>

   </ns0:protocol>

   </ns0:qualifier>

   <ns0:action></ns0:action>

   <ns0:direction>incomingPackets

   </ns0:direction>

   </ns0:rules>

   </ns0:trafficRuleset>

   </ns0:filterConfig>

   </ns0:filterPolicy>

   </ns0:setting>

   <ns0:configVersion>4</ns0:configVersion>

   </ns0:port>

   </ns0:ReconfigureDVPort_Task>

   </ns1:Body>

</SOAP-ENV:Envelope>

What I receive in answer is:

A general system error occurred: Not initialized

Can someone tell me what is wrong with my SOAP request. Maybe I have to configure something on DVS or Port Group, to make this SOAP request to work.

I'm using oslo.vmware to create and send API requests. DVS is set to be compatible with vSphere API 5.5.